The invention relates to an uninterruptible power supply system for use in high-power systems for organisations such as hospitals or large administrations, databanks, high technology industries, etc., which cannot suffer any disturbance to their electrical network without unacceptable damage.
In order to guarantee an uninterrupted power supply, “dynamic uninterruptible power supply” (DUPS) systems are frequently used. The DUPS systems generally comprise at least two essential components: a kinetic energy accumulator and a synchronous machine, where all the components are assembled on a common frame.
One such minimal configuration, for example, is that described in European Patent EP 1.533.884. This configuration makes it possible to provide a power supply generally in excess of 10 seconds, equivalent to the time required to start up an electricity generator unit which is connected electrically via a coupling device called a source inverter, to ensure continuity of supply.
In some cases, a diesel motor can be associated by providing a second shaft end to the kinetic energy accumulator or to an alternator and a temporary coupling system, for example, a clutch. In this latter configuration, the diesel motor is intended to pick up the load before the available energy in the kinetic energy accumulator has fully expended.
The systems described above must guarantee a very high degree of reliability, as they are employed for users who cannot suffer any disturbance to their electrical network.
The market for this type of dynamic uninterruptible power supply is growing rapidly due to the increased number and size of data centres and high technology industries. The instability of big electrical networks, caused by the use of alternative energies, is engendering a high demand for high-power systems for increasing the reliability for hospitals, large administrations, data centres, and high technology industries.
There is therefore a need for DUPS systems of increasingly large unit capacities, that allow the number of machines required to be reduced, thereby rendering installations simpler and significantly more economic. The DUPS systems described above are, however, limited in terms of capacity and autonomy by the kinetic energy accumulator. Kinetic energy accumulators are based on a concept whereby substantial large-diameter masses are in rotation at high speeds.
Because of this, the mechanical stresses induced in the parts rotating at high speeds limit both the diameter and the speed of rotation, in accordance with the law governing centrifugal forces f=m·w2·r. Another element to be considered is the total mass of the rotating part, which accumulates energy according to the law E=½ J·W2. This mass has to be supported by bearings and therefore the limits of the capacities of the bearings supplied by the main manufacturers in terms of load and service life are quickly reached.
In contrast, synchronous machines that are commonly and commercially available can easily achieve higher capacities than those of kinetic energy accumulators.